Use of polypeptides and proteins for the systemic treatment of specific diseases is now well accepted in medical practice. The role that these substances play in therapy is so important that many research activities are being directed towards the synthesis of large quantities by recombinant DNA technology. Many of these polypeptides are endogenous molecules which are very potent and specific in eliciting their biological actions.
A major factor limiting the usefulness of these proteinaceous substances for their intended application is that, when given parenterally, they are eliminated from the body within a short time. This can occur as a result of metabolism by proteases or by clearance using normal pathways for protein elimination such as by filtration in the kidneys. The oral route of administration of these substances is even more problematic because in addition to proteolysis in the stomach, the high acidity of the stomach destroys them before they reach their intended target tissue. The problems associated with these routes of administration of proteins are well known in the pharmaceutical industry, and various strategies are being used in attempts to solve them.
A great deal of work dealing with protein stabilization has been published. Various ways of conjugating proteins with polymeric materials are known, including use of dextrans, polyvinyl pyrrolidones, glycopeptides, polyethylene glycol and polyamino acids. The resulting conjugated polypeptides are reported to retain their biological activities and solubility in water for parenteral applications.
A peptide family which has been the focus of much clinical work, and efforts to improve its administration and bio-assimilation, is the interferons. Interferons have been tested in a variety of clinical disease states. The use of human interferon beta, one member of that family, is best established in the treatment of multiple sclerosis. Two forms of recombinant interferon beta, have recently been licensed in Europe and the U.S. for treatment of this disease. One form is interferon-beta-1a (trademarked and sold as AVONEX®, mfg. Biogen, Inc., Cambridge, Mass.) and hereinafter, “interferon-beta-1a” or “IFN-beta-1a” or “IFN-β-1a” or “interferon-β-1a”, used interchangeably. The other form is interferon-beta-1b (trademarked and sold as BETASERON®. Berlex, Richmond, Calif.), hereinafter, “interferon-beta-1b”. Interferon beta-1a is produced in mammalian cells using the natural human gene sequence and is glycosylated, whereas interferon beta-1b is produced in E. coli bacteria using a modified human gene sequence that contains a genetically engineered cysteine-to-serine substitution at amino acid position 17 and is non-glycosylated.
Previously, several of us have directly compared the relative in vitro potencies of interferon-beta-1a and interferon beta 1b in functional assays and showed that the specific activity of interferon-beta-1a is approximately 10-fold greater than the specific activity of interferon-beta-1b (Runkel et al., 1998, Pharm. Res. 15: 641-649). From studies designed to identify the structural basis for these activity differences, we identified glycosylation as the only one of the known structural differences between the products that affected the specific activity. The effect of the carbohydrate was largely manifested through its stabilizing role on structure. The stabilizing effect of the carbohydrate was evident in thermal denaturation experiments and SEC analysis. Lack of glycosylation was also correlated with an increase in aggregation and an increased sensitivity to thermal denaturation. Enzymatic removal of the carbohydrate from interferon-beta-1a with PNGase F caused extensive precipitation of the deglycosylated product.
These studies indicate that, despite the conservation in sequence between interferon-beta-1a and interferon-beta-1b, they are distinct biochemical entities and therefore much of what is known about interferon-beta-1b cannot be applied to interferon-beta-1a, and vice versa.